It showed the Islamist militants and girls in floor-length Islamic dress speaking to camera.

A video which Boko Haram claim show the missing Nigerian schoolgirls

Speaking for around 17 minutes Boko Haram's leader Abubakar Shekau said the girls have been converted to Islam and would not be released until Boko Haram prisoners are freed.

The girls are seen wearing black and grey Islamic dress called a chador (loose cloak) in an undisclosed rural location.

The group was founded in 2002 in Nigera's northeastern Borno district - where the schoolgirls may have been taken - and is committed to creating an Islamic state in Nigeria, where Sharia courts would dispense criminal justice.

Boko Haram - which means "Western education is sinful" - is only a nickname. Their preferred name is Jama'atu Ahlis Sunna Lidda'awati Wal-Jihad, which means "people committed to the propagation of the prophet's teachings and jihad".